1. Technical Field
The present invention relates to a touch display panel, and in particular, to an optical touch display panel.
2. Related Art
With the development of science and technologies, currently, a touch display panel is widely used as a man-machine data communication interface in many consumption electronic products (such as, personal digital assistants (PDAs), mobile phones, and tablet computers). The touch display panel may use different sensing technologies, such as resistive, capacitive, and optical sensing technologies, to detect the position where a user touches on the touch display panel.
FIG. 1 is a first schematic view of detection by a light-sensing touch display panel 100 according to the prior art. FIG. 2 is a second schematic view of detection by a light-sensing touch display panel 100 according to the prior art. FIG. 3 is a schematic view of light-sensing signals generated by a light-sensing component 110 when receiving light of different intensities according to the prior art.
As shown in FIG. 1, the light-sensing touch display panel 100 includes the light-sensing component 110, which is used for detecting change of an external light source. In a normal situation, the light-sensing component 110 detects an environment light L and generates a light-sensing signal S1 (see FIG. 3).
Please refer to FIG. 1, in which when a finger 120 contacts or gets close to the light-sensing touch display panel 100 and blocks the environment light L being received by the light-sensing component 110, the light-sensing component 110 correspondingly generates a light-sensing signal S2 (see FIG. 3).
Please refer to FIG. 2, in which when a light pen 130 gets close to or contacts the light-sensing touch display panel 100, the light-sensing component 110, in addition to receiving the environment light L, also receives light emitted by the light pen 130, and the light-sensing component 110 correspondingly generates a light-sensing signal S3 (see FIG. 3).
As shown in FIG. 3 for example, the light-sensing component 110 is a thin-film transistor (TFT). When a gate (G)-source (S) voltage (that is, Vgs) of the light-sensing component 110 is less than zero volt, the greater intensity of the light received by the light-sensing component 110 results in a greater drain-source current Ids.
FIG. 4 is a detection circuit diagram of the light-sensing component 110 according to the prior art. FIG. 5 is a schematic view of correspondence between a voltage level of a first end Va of a capacitor irradiated by different light sources and the gate-source voltage Vgs according to the prior art.
As shown in FIG. 4, the light-sensing component 110 is connected electrically to a storage capacitor Cs1. When the light-sensing component 110 generates different light-sensing signals (that is, drain-source currents Ids), as a result of detecting different light sources, the voltage level of the first end Va of the storage capacitor Cs1 decreases accordingly. The voltage level of the first end Va of the storage capacitor Cs1 can be used to determine whether a touch input is made.
It is taken as example that the light pen 130 shown in FIG. 2 is used for making a touch input. Before a touch input is made, the light-sensing component 110 is only irradiated by the environment light L, so that a reading signal Ro generated by the voltage level of the first end Va of the storage capacitor Cs1 is a dark state voltage V1 (see FIG. 5). When a touch input is made, the light-sensing component 110, in addition to receiving the environment light L, also receives the light emitted by the light pen, so that the reading signal Ro is a bright state voltage V2 (see FIG. 5). Whether a touch input is made can be determined by determining whether a voltage difference ΔV between the bright state voltage V2 and the dark state voltage V1 exceeds a predetermined threshold value.
After the voltage of the first end Va of the storage capacitor Cs1 reaches a level, in order to detect a touch input once again, the voltage of the storage capacitor Cs1 must be reset, that is, the storage capacitor Cs1 must be charged so that the voltage thereof reaches a reset voltage. However, to synchronize a touch interface with a display image, a touch detection frequency is generally the same as a screen update frequency (that is, a frame rate). Being restricted by the frame rate, the time for charging the storage capacitor Cs1 (referred to as a “reset time” for short below), is limited, so that a reset voltage level of the storage capacitor Cs1 is not high enough, which results in a low dark state voltage level. When the bright state voltage level is fixed, the voltage difference ΔV is small, which causes a low signal-to-noise ratio, thereby easily resulting in false determination in the detection of a touch event.